Nanoscopic Terraces, Mesas, and Ridges in Freely Standing Thin Films Sculpted by Supramolecular Oscillatory Surface Forces

Abstract

Freely standing thin liquid films containing supramolecular structures including micelles, nanoparticles, polyelectrolyte-surfactant complexes, and smectic liquid crystals undergo drainage via stratification. The layer-by-layer removal of these supramolecular structures manifests as stepwise thinning over time and a coexistence of domains and nanostructures of discretely different thickness. The layering of supramolecular structures in confined thin films contributes additional non-DLVO, supramolecular oscillatory surface forces to disjoining pressure, thus influencing both drainage kinetics and stability of thin films. Understanding and characterizing the spontaneous creation and evolution of nanoscopic topography of stratifying, freely standing thin liquid films have been long-standing challenges due to the absence of experimental techniques with the requisite spatial (thickness <10 nm) and temporal resolution (<1 ms). Using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols developed herein, we visualize and characterize size, shape, and evolution kinetics of nanoscopic mesas, terraces, and ridges. The exquisite thickness maps created using IDIOM protocols provide much needed and unprecedented insights into the role of supramolecular oscillatory surface forces in driving growth of such nanostructures as well as in controlling properties and stability of freely standing thin films and, more generally, of colloidal dispersions like foams.

Thin film drainage dynamics of wheat and rye dough liquors and oat batter liquor

“…the black regions). A similar effect has been observed for sodium dodecyl sulfate (SDS) TFs Zhang et al 2016).…”

“…The magnitude of Πsup at these metastable TF thicknesses generally increases as the number of micellar layers decreases and can reach values up to 200 Pa (Zhang and Sharma, 2018) or even 1,000 Pa (Basheva et al 2007). However, the magnitude of Πsup at such metastable thicknesses is system-specific and amongst others depends on the molecular structure and concentration of the involved surfactants (Basheva et al 2007;Zhang et al 2016). Nonetheless, earlier it was mentioned that gas cells in bread dough at the end of fermentation may experience PL, gas cell values lower than 200 Pa.…”

Foam film stratification studies probe intermicellar interactions

“…M olecules in simple liquids and supramolecular structures in complex fluids can stratify or undergo confinement-induced layering induced by symmetry breaking at a solid-liquid or a fluidfluid interface (1)(2)(3)(4)(5)(6)(7)(8). In freestanding or foam films, the confinementinduced layering of supramolecular structures including micelles (9)(10)(11)(12)(13)(14)(15)(16)(17), lipid layers (18,19), polyelectrolyte-surfactant complexes (20,21), nanoparticles (9,22), and liquid crystalline assemblies (23) can result in drainage via stratification. Due to thin film interference, foam films visualized under white light illumination display iridescent colors for thick films (h > 100 nm) (24)(25)(26)(27)(28), but ultrathin films (h < 100 nm) exhibit shades of gray that get progressively darker as the film gets thinner (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21).…”

“…In freestanding or foam films, the confinementinduced layering of supramolecular structures including micelles (9)(10)(11)(12)(13)(14)(15)(16)(17), lipid layers (18,19), polyelectrolyte-surfactant complexes (20,21), nanoparticles (9,22), and liquid crystalline assemblies (23) can result in drainage via stratification. Due to thin film interference, foam films visualized under white light illumination display iridescent colors for thick films (h > 100 nm) (24)(25)(26)(27)(28), but ultrathin films (h < 100 nm) exhibit shades of gray that get progressively darker as the film gets thinner (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). In reflected light microscopy, micellar foam films exhibit coexisting thick−thin regions with distinct shades of gray.…”

Mimicking coalescence using a pressure-controlled dynamic thin film balance

“…10,14,15 More recently, it was used to study the complex interplay between hydrodynamics and dynamic deformation of surfaces that results in effects such as the formation of a dimple formation, 16 evolution of fluctuations, 17 spatiotemporal changes in surface stresses 18 and a wide range of instabilities. [19][20][21][22][23] So far almost all of the TFB studies involved the drainage of TLFs under a small constant pressure, which is controlled by the radius of the cavity where the film is formed. Two notable exceptions exist, 24,25 which involved the forced drainage of foam films due to an extra pressure or flow rate applied by a syringe pump.…”